Nonadiabatic high-Tc superconductivity in hole-doped fullerenes

In this paper we address the possibility of high-T-c superconductivity (T(c)similar to100 K) in hypothetical hole doped C-60 within the context of the nonadiabatic theory of superconductivity. Our analysis shows that electron doped fullerenes, represented by the A(3)C(60) family, are characterized by relatively small values of the electron-phonon coupling constant lambda, which can thus be further increased by hole doping before lattice instabilities occur. In particular we show that T-c larger than 100 K are compatible in the nonadiabatic context with microscopic parameters lambda(h)similar or equal to0.5-1.0, mu(*)similar or equal to0.3-0.5 and phonon frequencies omega(ph)similar or equal to1500-2000 K. These results provide a stimulus for material engineering and optimization along the lines indicated

Folded Supersymmetry and the LEP Paradox

We present a new class of models that stabilize the weak scale against radiative corrections up to scales of order 5 TeV without large corrections to precision electroweak observables. In these `folded supersymmetric' theories the one loop quadratic divergences of the Standard Model Higgs field are cancelled by opposite spin partners, but the gauge quantum numbers of these new particles are in general different from those of the conventional superpartners. This class of models is built around the correspondence that exists in the large N limit between the correlation functions of supersymmetric theories and those of their non-supersymmetric orbifold daughters. By identifying the mechanism which underlies the cancellation of one loop quadratic divergences in these theories, we are able to construct simple extensions of the Standard Model which are radiatively stable at one loop. Ultraviolet completions of these theories can be obtained by imposing suitable boundary conditions on an appropriate supersymmetric higher dimensional theory compactified down to four dimensions. We construct a specific model based on these ideas which stabilizes the weak scale up to about 20 TeV and where the states which cancel the top loop are scalars not charged under Standard Model color. Its collider signatures are distinct from conventional supersymmetric theories and include characteristic events with hard leptons and missing energy.Comment: 18 pages, 5 figures, references correcte

APEX: A Prime EXperiment at Jefferson Lab

APEX is an experiment at Thomas Jefferson National Accelerator Facility (JLab) in Virginia, USA, that searches for a new gauge boson ($A^\prime$) with sub-GeV mass and coupling to ordinary matter of $g^\prime \sim (10^{-6} - 10^{-2}) e$. Electrons impinge upon a fixed target of high-Z material. An $A^\prime$ is produced via a process analogous to photon bremsstrahlung, decaying to an $e^+ e^-$ pair. A test run was held in July of 2010, covering $m_{A^\prime}$ = 175 to 250 MeV and couplings g^\prime/e \; \textgreater \; 10^{-3}. A full run is approved and will cover $m_{A^\prime} \sim$ 65 to 525 MeV and g^\prime/e \; \textgreater \; 2.3 \times10^{-4}.Comment: Contributed to the 8th Patras Workshop on Axions, WIMPs and WISPs, Chicago, July 18-22, 2012. 4 pages, 4 figure

QCD String as Vortex String in Seiberg-Dual Theory

We construct a classical vortex string solution in a Seiberg-dual theory of N=1 supersymmetric SO(N_c) QCD which flows to a confining phase. We claim that this vortex string is a QCD string, as previouly argued by M.Strassler. In SO(N_c) QCD, it is known that stable QCD strings exist even in the presence of dynamical quarks. We show that our vortex strings are stable in the Seiberg-dual theory.Comment: 15 pages, 1 figur

Adjoint Trapping: A New Phenomenon at Strong 't Hooft Coupling

Adding matter of mass m, in the fundamental representation of SU(N), to N=4 supersymmetric Yang-Mills theory, we study ``generalized quarkonium'' containing a (s)quark, an anti(s)quark, and J massless (or very light) adjoint particles. At large 't Hooft coupling $\lambda$ >> 1, the states of spin <= 1 are surprisingly light (Kruczenski et al., hep-th/0304032) and small (hep-th/0312071) with a J-independent size of order $\sqrt{\lambda}/m$. This ``trapping'' of adjoint matter in a region small compared with its Compton wavelength and compared to any confinement scale in the theory is an unfamiliar phenomenon, as it does not occur at small $\lambda$. We explore adjoint trapping further by considering the limit of large J. In particular, for J >> $\sqrt{\lambda}$ >> 1, we expect the trapping phenomenon to become unstable. Using Wilson loop methods, we show that a sharp transition, in which the generalized quarkonium states become unbound (for massless adjoints) occurs at $J \simeq 0.22 \sqrt{\lambda}$. If the adjoint scalars of N=4 are massive and the theory is confining (as, for instance, in N=1* theories) then the transition becomes a cross-over, across which the size of the states changes rapidly from ~$\sqrt{\lambda}/m$ to something of order the confinement scale ~ $\Lambda^{-1}$.Comment: Clarified transition with a better figure and improved presentation; added careful discussion of the small regime of validity of the Born-Oppenheimer computation and adjusted some remarks appropriately; also added two reference

Duality cascades and duality walls

We recast the phenomenon of duality cascades in terms of the Cartan matrix associated to the quiver gauge theories appearing in the cascade. In this language, Seiberg dualities for the different gauge factors correspond to Weyl reflections. We argue that the UV behavior of different duality cascades depends markedly on whether the Cartan matrix is affine ADE or not. In particular, we find examples of duality cascades that can't be continued after a finite energy scale, reaching a "duality wall", in terminology due to M. Strassler. For these duality cascades, we suggest the existence of a UV completion in terms of a little string theory.Comment: harvmac, 24 pages, 4 figures. v2: references added. v3: reference adde

Anarchy and Hierarchy

We advocate a new approach to study models of fermion masses and mixings, namely anarchy proposed in hep-ph/9911341. In this approach, we scan the O(1) coefficients randomly. We argue that this is the correct approach when the fundamental theory is sufficiently complicated. Assuming there is no physical distinction among three generations of neutrinos, the probability distributions in MNS mixing angles can be predicted independent of the choice of the measure. This is because the mixing angles are distributed according to the Haar measure of the Lie groups whose elements diagonalize the mass matrices. The near-maximal mixings, as observed in the atmospheric neutrino data and as required in the LMA solution to the solar neutrino problem, are highly probable. A small hierarchy between the Delta m^2 for the atmospheric and the solar neutrinos is obtained very easily; the complex seesaw case gives a hierarchy of a factor of 20 as the most probable one, even though this conclusion is more measure-dependent. U_{e3} has to be just below the current limit from the CHOOZ experiment. The CP-violating parameter sin delta is preferred to be maximal. We present a simple SU(5)-like extension of anarchy to the charged-lepton and quark sectors which works well phenomenologically.Comment: 26 page

Electroweak and Dark Matter Constraints on a Z' in Models with a Hidden Valley

We consider current precision electroweak data, Z' searches and dark matter constraints and analyse their implications for an extension of the SM that includes an extra U(1)' massive gauge boson and a particular hidden sector ("hidden valley") with a confining (QCD-like) gauge group. The constraints on the Z' with arbitrary Z-Z' kinetic mixing coming from direct searches and precision tests of the Standard Model are analysed and shown to lead to a lower limit of 800 GeV on its mass. Renormalisable interactions involving the Z' probe the physics of the hidden valley sector which contains a pseudoscalar dark matter candidate. We find that dark matter constraints place an upper bound on the mass of the Z' of O(10) TeV. A TeV mass scale is needed for the hidden valley states, and the Sommerfeld factor for p-wave dark matter annihilation is found significantly to suppress the allowed parameter space of the model.Comment: 35 pages, 14 figure

Stealth Supersymmetry

We present a broad class of supersymmetric models that preserve R-parity but lack missing energy signatures. These models have new light particles with weak-scale supersymmetric masses that feel SUSY breaking only through couplings to the MSSM. This small SUSY breaking leads to nearly degenerate fermion/boson pairs, with small mass splittings and hence small phase space for decays carrying away invisible energy. The simplest scenario has low-scale SUSY breaking, with missing energy only from soft gravitinos. This scenario is natural, lacks artificial tunings to produce a squeezed spectrum, and is consistent with gauge coupling unification. The resulting collider signals will be jet-rich events containing false resonances that could resemble signatures of R-parity violation. We discuss several concrete examples of the general idea, and emphasize gamma + jet + jet resonances, displaced vertices, and very large numbers of b-jets as three possible discovery modes.Comment: 12 pages, 4 figure

Comments on Condensates in Non-Supersymmetric Orbifold Field Theories

Non-supersymmetric orbifolds of N=1 super Yang-Mills theories are conjectured to inherit properties from their supersymmetric parent. We examine this conjecture by compactifying the Z_2 orbifold theories on a spatial circle of radius R. We point out that when the orbifold theory lies in the weakly coupled vacuum of its parent, fractional instantons do give rise to the conjectured condensate of bi-fundamental fermions. Unfortunately, we show that quantum effects render this vacuum unstable through the generation of twisted operators. In the true vacuum state, no fermion condensate forms. Thus, in contrast to super Yang-Mills, the compactified orbifold theory undergoes a chiral phase transition as R is varied.Comment: 10 Pages. Added clarifying comments, computational steps and a nice pretty pictur